Sealing structure for polymer electrolyte fuel cell

ABSTRACT

The present invention relates to a sealing structure for polymer electrolyte fuel cell, which comprises a bipolar plate with sealing groove to be filled with rubber using a dispenser, and a gasket interposed between the bipolar plate and a membrane electrode assembly. That is, according to the present invention, the thickness deviation in a gasket can be softened by interposing a gasket between a rubber ands a membrane electrode assembly after filling rubber in a sealing groove formed on a bipolar plate using a dispenser. Also, nonuniform stress distribution can be resolved because a gasket covers with a pressure despite the height deviation of rubber, and a stress is not directly transmitted to a membrane electrode assembly and dispersed by a gasket despite nonuniform stress distribution.

FIELD OF THE INVENTION

The present invention relates to a sealing structure for polymerelectrolyte fuel cell, and more particularly to the sealing structurefor polymer electrolyte fuel cell to prevent reaction gas or coolantetc. from leaking through the commissure between a bipolar plate and amembrane electrode assembly.

BACKGROUND OF THE INVENTION

In general, a polymer electrolyte fuel cell generates electricity andheat by electrochemically reacting a fuel gas containing hydrogen and anoxidizer gas containing oxygen. The polymer electrolyte fuel cell iscapable of working at a low temperature of 70-80° C. and of maintaininggreat current density. In these reasons, the polymer electrolyte fuelcell has fast startup performance, can be miniaturized, and can be madeinto light weight cells, thus suitable for use in such applications asportable power source, power source for vehicles, residential equipmentsof steam supply and power generation, etc.

FIG. 1 illustrates an embodiment of the polymer electrolyte fuel cell,which comprises a membrane electrode assembly (MEA, 10) comprising apolymer electrolyte membrane and an electrode, a gas diffusion layer(fluid distribution layer, 12) delivering the gas used in a reaction tothe electrode and discharging the reaction products, a conductivebipolar plate (separator, 14) supplying a reaction gas and a coolantfrom outside and separating oxidized electrode (anode) from deoxidizedelectrode (cathode), and the like. A fuel cell is composed by stackingthese membrane electrode assembly, gas diffusion layer and bipolar plateas many as necessary, and the stack forms a single body with anappropriate pressure given from outside by a equipment, so each unitcell is not out of line or slipped.

Also, a number of manifolds (20) are formed in the upper part and thelower part of the membrane electrode assembly (10) and the bipolar plate(14) for supplying or discharging hydrogen, oxygen needed in a reaction,and coolant needed to cool the reaction heat. And hydrogen, oxygen andcoolant supplied from outside are taken into the electrode passingthrough a pipe outside the stack, the manifold of the bipolar plate, anda gas-flow path formed on the bipolar plate of each unit cell.

On the other hand, a sealing means should be included to preventhydrogen, oxygen and coolant from leaking from each manifold and thereaction site where hydrogen and oxygen react. However, in the fuelcell, often stopping are repeated by its own characteristics, andexpansion and contraction are frequently occurred during the fuel celloperation because of the heat generated by the chemical reaction.Therefore, a sealing structure for the fuel cell must exert sealingperformance in the case of frequent expansion and contraction, and onlyif the stress distribution arising in each element of fuel cell inexpansion and contraction is as uniform as possible, the fatigue failurecan be prevented.

For this, a gasket is disposed around the electrode and manifold. As agasket for sealing the fuel cell, silicon sheet or Teflon sheetstrengthened by glass fibers is often used because of its easymanufacturing advantage and little thickness deviation.

This strengthened silicon sheet or Teflon sheet has an excellentmechanical strength supported by internal glass fibers, so it can exertmechanical toughness under the excessive pressure in the time when astack is bound. But the rate of contraction and restoration are not sohigh that, when the fuel cell operates, gas is apprehended to leak forthe expansion of parts by heat and water Moreover gas can leak throughthe surface of the gasket because the surface is rough and the materialis relatively hard.

Another defect is that, if formed thicker than a gas diffusion layerwhen a stack is bound, the resistance increases because the mechanicalstrength is greater than that of a carbon paper or a carbon clothgenerally used as a gas diffusion layer, and the contact between a gasdiffusion layer and a bipolar plate is not tight. On the contrary, thereis a problem that, if formed too thin, gas leaks because the pressure onthe surface of the gasket is not enough. Therefore it is difficult todetermine the proper thickness.

Another way for sealing the fuel cell is to use rubber with superiorelastic restitution force and soft property containing silicon, fluorineor olefin as a material of a gasket. There are the way of manufacturinga gasket in the shape of O-ring using a metal mold, the way of jetmolding with a metal mold being placed directly on a bipolar plate, andthe way of manufacturing a gasket using a dispenser, etc in the way ofmanufacturing a gasket of rubber.

The way of manufacturing a gasket in the shape of O-ring using a metalmold has the defect that, after manufacturing a gasket, it must beplaced on the surface of a bipolar plate one by one when a stack isbound. And the way of jet molding with a metal mold being placeddirectly on a bipolar plate has the defect that, in the time ofmanufacturing a gasket, the shape and the dimension of a metal mold mustbe same with the gasket.

Also, the conventional way of manufacturing a gasket using a dispenseris the way of putting sealant in an injector and the like and pressingit, so has the problem that the height of rubber at starting point andending point cannot be set uniformly. That is, the liquid state ofrubber material is filled along a route of a sealing groove using adispenser operated by X-Y axis robot, after forming the sealing groovein advance on a bipolar plate, with a width and a depth. The rubberoverlaps in ending point with that of starting point, so height becomegreater than that of other part.

Hereby the pressure of the surface on the bipolar plate and the membraneelectrode assembly become nonuniform when a stack is bound, so not onlysealing performance is lowered but also the life span of fatigue failureis shortened by this nonuniform stress distribution when used in thecase of long term repeatedly.

SUMMARY OF THE INVENTION

The present invention was invented to overcome the defects ofconventional technologies, and it is an object of the present inventionto provide a sealing structure for polymer electrolyte fuel cell whosestructure not only does not lower the sealing performance although thethickness deviation of a gasket occurs, but also can disperse nonuniformstress distribution onto a bipolar plate and a membrane electrodeassembly.

It is another object of the present invention to provide a sealingstructure for polymer electrolyte fuel cell wherein rubber can be filledin a sealing groove formed on a bipolar plate using a dispensercomparatively easy to handle, to have entirely uniform height, toimprove sealing performance by preventing the nonuniform pressure on asurface, and to extend the life span of products.

To solve above technical problem, the present invention comprises abipolar plate with sealing groove to be filled with rubber using adispenser; and a gasket interposed between the bipolar plate and amembrane electrode assembly.

That is, according to the present invention, the thickness deviation ina gasket can be softened by interposing a gasket between a rubber and amembrane electrode assembly after filling rubber in a sealing grooveformed on a bipolar plate using a dispenser. Also, nonuniform stressdistribution can be resolved because a gasket covers with a pressuredespite the height deviation of rubber, and a stress is not directlytransmitted to a membrane electrode assembly and dispersed by a gasketdespite nonuniform stress distribution.

It is desirable that the sealing groove is formed in the perimeter ofthe reaction site of bipolar plate, and the perimeter of the manifold ofhydrogen, oxygen and coolant as well.

On the other hand, in the case of using a dispenser, because thedifference of height between at starting point and at ending point isrelatively greater than that of other parts, it is desirable to furthercomprise an anchor in contact with the sealing groove, whose width isgreater than the width of the sealing groove.

That is, by filling rubber by controlling a dispenser to start from theanchor and end in the anchor, the height of starting point and endingpoint can be uniform. And the width of the anchor is wide enough,although the height increases temporarily by the partial overlapping ofstarting point with ending point, the height becomes uniform by thediffusing of rubber right and left.

It is preferable that the anchor has a width of 1.5 times of the widthof the sealing groove. Thereby, damaging the sealing performance, withthe rubber being diffused excessively and thinner than that of sealinggroove, can be prevented effectively.

Also, it is desirable that the sealing groove and the anchor have samedepth, for a dispenser to move at uniform speed. Because, in the casethat the depth of an anchor is different from the depth of sealinggroove, the nonuniform moving speed of a dispenser can be brought aboutto fill up to the surface of groove.

On the other hand, an anchor can be located anywhere only if it iscontacted with the sealing groove. That is, by expanding the partialwidth of sealing groove right and left, an anchor can be formed. But, itis more desirable that the anchor is formed vertically to a routedirection of the sealing groove in the periphery of the sealing groove.

That is, on the characteristic of working, the height of rubber filledin an anchor portion is greater than the height of rubber filled in asealing groove portion, and when the bipolar plate is bound to a fuelcell stack relatively more force is given to the perimeter of a bipolarplate than inner part. Therefore, by forming an anchor in the peripheryof sealing site, the pressure given to the perimeter can be absorbedeffectively, and consequently the pressure given to the entire bipolarplate can be distributed uniformly. In this respect, it is moredesirable that the anchors on each of the bipolar plate located in thefront and the rear of said membrane electrode assembly, are locatedsymmetrically to each other when a fuel cell bound to a stack.

On the other hand, the rubber is made of any of rubber materialscontaining silicon, fluorine or olefin.

Also, it is desirable that the gasket is manufactured of the samematerial with the bipolar plate by this the deformation and nonuniformstress distribution caused by the difference of heat expansion rate canbe prevented.

Also, the present invention includes a polymer electrolyte fuel cellcomprising the sealing structure above-mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view for illustrating generalstructure of polymer electrolyte fuel cell.

FIG. 2 is a front side elevation view illustrating bipolar plate in anembodiment of sealing structure of polymer electrolyte fuel cellaccording to the present invention.

FIG. 3 is a perspective view illustrating A portion in FIG. 2 enlarged.

FIG. 4 is a view equivalent to FIG. 1 illustrating polymer electrolytefuel cell applied to by bipolar plate illustrated in FIG. 2.

FIG. 5 is a vertical cross section view illustrating the pre-assembledstate of polymer electrolyte fuel cell illustrated in FIG. 4.

FIG. 6 is a vertical cross section view illustrating the assembled stateof polymer electrolyte fuel cell illustrated in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of polymer electrolyte fuel cell according tothe present invention will be described in more detail with reference tothe accompanying drawings. Also, in the present invention, the basicfunctional principle and process of fuel cell are same with that ofconventional things, so the explanation for these is omitted.

Referring to FIG. 2, in the central part of Bipolar plate 100 of theembodiment, a reaction site 102 where hydrogen reacts with oxygen isformed, in the upper part manifold 104, 106, 108 are formed where eachof hydrogen, oxygen and coolant is supplied. Also, in the lower partmanifold 104′, 106′, 108′ to discharge each of coolant, oxygen andhydrogen are formed.

The Bipolar plate 100 plays the role that hydrogen and oxygen do notmixed in a fuel cell, and that membrane electrode assembly is connectedelectrically, and functions as mechanical supporter of stacked unitcells. Also it functions that reaction gas flows to electrode evenly,membrane is not dry through adequate water management, and water createdin deoxidation electrode is discharged. As the material of bipolar plate100 graphite or carbon composite can be used, and also metallic plate isused. In the case of metallic plate is used, it can be eroded so it isnecessary to coat the surface with high-conductive, anticorrosivematerial. In this embodiment carbon composite is used as bipolar plate100.

On the other hand, in the perimeter of the reaction site and eachmanifold, sealing grooves 110, 110′ are formed, in FIG. 2 and FIG. 3 thesealing grooves filled with rubber are illustrated. Here, in the lowerleft part of the sealing groove 110 located in a reaction site, theanchor 112 which has the width of 1.5 times of the width of the sealinggroove 110 is formed to be extended toward the outside of bipolar plate100. The sealing groove and the anchor can be formed by CNC processingor press metallic pattern etc., the sealing groove 110 is formed to havethe depth of 0.3 mm and the width of 2 mm in the illustrated embodiment,and the anchor 112 is formed to have the depth of 0.3 mm and the widthof 3 mm. In this time, rubber is discharged from a dispenser (notillustrated) with the width of 1.2 mm and the height of 0.60 mm. Thatis, rubber is filled in a sealing groove in the state of partiallyprojected from the surface of bipolar plate, and the definite dimensionof a sealing groove and an anchor is changeable according to therequired capacity and the size of fuel cell.

As illustrated in FIG. 3, if the filling work of rubber start from theanchor 112 and finish in the anchor 112, because the anchor is formedwidely enough, although the height of rubber filled in is nonuniform, itis diffused right and left, the starting point overlap with the endingpoint, and the height of the rubber becomes uniform.

After rubber is filled in a sealing groove and an anchor, if bipolarplate is heat-treated in the oven of 100° C. for 30 minutes, liquidrubber dried into solid. On the other hand, rubber is filled in theperimeter of the hydrogen, oxygen and coolant manifold as well in thesame way with above.

Referring to FIG. 4-6, ordinary membrane electrode assembly 300 islocated in the center of a fuel cell using above bipolar plate 100, acouple of gasket 200, 200′ are in contact with the front and rear sideof membrane electrode assembly 300, bored in the portion of 202, 204,206, 208, 206′, 208′ each corresponding to the reaction site 102,hydrogen, oxygen and coolant manifold 104, 106, 108, 104′, 106′, 108′,and a couple of the bipolar plate 100, 100′ are adhered to the outside.

A couple of gas diffusion layer. 310, 310′ are adhered to the centralfront and rear side of the membrane electrode assembly 300, and the edgeof the portion 202 of the gasket 200 corresponding to reaction site isadhered to, in contact, the side of the gas diffusion layer 310, somembrane electrode assembly 300 function as structural supporter touniform the entire thickness. Above hydrogen, oxygen and coolantmanifold 304, 306, 308 are formed in the upper and lower part ofmembrane electrode assembly 300.

In FIG. 5 the rubber 110, 110′ is projected from the surface in acertain amount, but in the assembled state illustrated in FIG. 6 therubber maintains the state of pressed and adhered by the surface of thegasket 200, so the leakage can be prevented by the rubber although thethickness of gasket is nonuniform. Also, not because the stress given bythe counter-force from the press of rubber is not directly transmittedto membrane electrode assembly, but because it is transmitted uniformlydiffused through the gasket, the deformation and the destruction bynonuniform stress distribution is prevented.

Industrial Applicability

According to the present invention comprised as above mentioned, notonly sealing performance is highly improved because a rubber and agasket seal doubly, but also in the case the surface of rubber or gasketis nonuniform it is buffered and supplemented by the interaction, it isa merit that if used for long term repeatedly, initial sealingperformance can be maintained as it is.

That is, although the deviation is occurred in the thickness of agasket, it is in contact with the rubber partially projected from abipolar plate, and the minuteness can be lowered in the time of gasketprocessing, so not only manufacturing cost can be reduced but alsodesign can be accomplished more flexibly. And, in the case that thesurface of rubber discharged by a dispenser is nonuniform, not onlyperfect sealing is possible because it is assembled in the state thatthe surface of a gasket is compressed but also the problem by nonuniformstress distribution can be minimized because the stress generated byrubber, even if not uniform, is transmitted to membrane electrodeassembly diffused through gasket.

Also, by setting up an anchor in a part of a sealing groove filled withrubber, there is an effect that not only height deviation in thestarting point and the ending point of rubber filled by a dispenser canbe minimized, but also production cost can be reduced by reducing theloss of the rubber material.

What is claimed is:
 1. A sealing structure for polymer electrolyte fuelcell having a membrane electrode assembly, the sealing structurecomprising: a bipolar plate including a sealing groove and an anchorgroove coupled to a periphery of the sealing groove, the sealing groovesurrounding at least one of a reaction site or a manifold formed on thebipolar plate, the anchor groove extending toward an outer edge of thebipolar plate, and a width of the anchor groove being greater than awidth of the sealing groove; a sealing member formed of rubber andpositioned in the sealing groove and the anchor groove; and a gasketplate interposed between the bipolar plate and the membrane electrodeassembly, wherein the sealing member is formed by drying liquid rubber,the liquid rubber filling in the sealing groove by controlling adispenser to start from the anchor groove and finish in the anchorgroove by way of the sealing groove.
 2. The sealing structure as inclaim 1, wherein the width of the anchor groove is 1.5 times greaterthan the width of the sealing groove.
 3. The sealing structure as inclaim 2, wherein a depth of the sealing groove is equal to a depth ofthe anchor groove.
 4. The sealing structure as in claim 1, wherein theanchor groove is formed extending from the periphery of the sealinggroove along a direction perpendicular to the periphery of the sealinggroove.
 5. The sealing structure as in claim 1, further comprising anopposed bipolar plate having an opposed anchor groove, wherein thebipolar plate and the opposed bipolar plate are disposed on oppositesides of the membrane electrode assembly.
 6. The sealing structure as inclaim 1, wherein the rubber comprises a rubber material containing atleast one of silicon, fluorine, or olefin.
 7. The sealing structure asin claim 1, wherein the gasket plate comprises the same material as thebipolar plate.
 8. A polymer electrolyte fuel cell comprising saidsealing structure stated in any of claims 1 and 2-7.
 9. The sealingstructure of claim 5, wherein the opposed anchor groove is formed on theopposed bipolar plate at a location symmetric with respect to the anchorgroove of the bipolar plate.